The production of normal paraffins provides the ability for upgrading products from straight runs of hydrocarbon streams derived from crude oil fractionation. In particular, straight run kerosene is further processed to separate out normal paraffins for higher valued products, such as used in the production of linear alkylbenzenes (LAB). Normal paraffins in the range of C10 to C13 are important precursors to LAB production, which is in turn used to produce linear alkylbenzene sulfonate (LAS). LAS is the predominant surfactant used in the production of detergents.
The large utility of detergents and other cleaners has led to extensive development in the areas of detergent production and formulation. While detergents can be formulated from a wide variety of different compounds much of the world's supply is formulated from chemicals derived from alkylbenzenes. The compounds are produced in petrochemical complexes in which an aromatic hydrocarbon, typically benzene, is alkylated with an olefin of the desired structure and carbon number for the side chain. Typically the olefin is actually a mixture of different olefins forming a homologous series having a range of three to five carbon numbers. The olefin(s) can be derived from several alternative sources. For instance, they can be derived from the oligomerization of propylene or butenes or from the polymerization of ethylene. Economics has led to the production of olefins by the dehydrogenation of the corresponding paraffin being the preferred route to produce the olefin.
The choice of carbon numbers is set by the boiling point range of straight run cuts from crude distillation. Kerosene boiling range fractions from crude oil provide heavier paraffins. Paraffins having 8 to 15 carbons are present in significant concentrations in relatively low cost kerosene. These paraffins have been a predominant source for linear alkanes and the leading source of olefin precursors for use in making LABs. Recovery of the desired normal paraffins from kerosene is performed by adsorption separation, which is one process in overall production of LABs. The paraffins are then passed through a catalytic dehydrogenation zone wherein some of the paraffins are converted to olefins. However, the paraffin dehydrogenation also generates heavy aromatics which are undesirable. Thereafter, the resulting effluent from the paraffin dehydrogenation zone is passed through an aromatic removal zone for selective removal of aromatics before passing the feed to the downstream alkylation zone in which the olefins are reacted with the aromatic substrate.
Typically, the aromatics removal zone in the LAB production process, includes a plurality of adsorbers along with a desorbent column. The plurality of adsorbers are regenerated subsequent to adsorption using a regenerant stream such as a benzene stream. In the desorbent column, heavy aromatics are removed from the spent regenerant stream comprising the heavy aromatics. Currently, the desorbent column require a large amount of hot oil duty to reboil desorbent benzene in order to remove a small amount of heavy aromatics. Typically, less than 10% of the desorbent column feed is taken out as a bottoms stream, which causes unreasonable product split and issues in column design.
Accordingly, it is desirable to provide an improved process for separation of heavy aromatics from a spent regenerant stream. It is desirable for the instant process to have reasonable product split for the desorbent column. It is also desirable to minimize hot oil duty required in fractionating the heavy aromatics in the spent regenerant stream in such apparatuses. Other desirable features and characteristics of the present subject matter will become apparent from the subsequent detailed description of the subject matter and the appended claims, taken in conjunction with the accompanying drawing and this background of the subject matter.